1. Field of the Invention
The present invention relates to an organic electrolytic solution cell, and more particularly, it relates to an improvement of the organic electrolytic solution of such cell.
2. Description of the Related Art
The organic electrolytic solution cell, such as a lithium-manganese-dioxide cell which comprises a lithium negative electrode, a manganese dioxide positive electrode and an organic electrolytic solution, has increasingly come into wide use, because of its high energy density, light weight and long-life.
As an electrolyte for the organic electrolytic solution cell, LiClO.sub.4 is commonly used. (See, for example, T. Iwamaru, O. Kajii, Practical Lithium Batteries, p53 (1988).
A cylindrical lithium-manganese dioxide cell has also increasingly come into wide use as a battery of a camera. Combinations of the electrolytic solution such as a cyclic ether and the electrolyte have been studied in order to provide excellent characteristics even at a low temperature.
Consideration as to safety is important for a big size cell such as the cylindrical lithium-manganese dioxide cell, because it is dangerous if a fire or a detonation occurs by any chance.
Generally, this type of the cell is provided with the PTC device a resistance of which increases to decrease the intensity of an electric current when a temperature of the cell rises abnormally by an electric current or heat or a safety valve device, which exhausts the inner gas in the cell through a vent hole to prevent explosion of the cell under high pressure, when an inner pressure of the cell is increased abnormally by generation of gas in the cell. However, the cell may be fired after continuation of the overdischarge under a large electric current without the PTC device.
For example, the cylindrical lithium-manganese dioxide cell comprising LiClO.sub.4 as the electrolyte, as shown in FIG. 1, which has an outer diameter of 15 mm and a height of 40 mm, abnormally generates heat when it is overdischarged at 4 A and discharged at a constant voltage of -3 V after reaching -3 V, and sometime causes the fire or the detonation.
To improve the thermal stability of the cell, it is proposed to use LiCF.sub.3 SO.sub.3 as an electrolyte. Though the cell using LiCF.sub.3 SO.sub.3 is stable under the normal condition, it generates abnormal heat when the discharge electric current exceeds 15 A.
Therefore the use of LiCF.sub.3 SO.sub.3 which effects to the safety only in the overdischarge is still insufficient.